1. Field of the Invention
The present invention relates to an optical disk apparatus and an optical pickup device mounted thereon, particularly to an optical disk apparatus in which an objective lens made of a resin material is suitably incorporated in an optical pickup device.
2. Description of the Related Art
Conventionally, the objective lens incorporated in the optical pickup device is made of a glass material. However, disadvantageously the objective lens made of the glass material is expensive, and a response characteristic of the optical pickup is hardly enhanced because the glass material has a large specific gravity. By contrast, when the objective lens is made of a resin material, cost of the objective lens can be largely reduced compared with the objective lens made of the glass material. Additionally because the resin material is about half the specific gravity of the glass material, the resin material can realize weight reduction and high-response of the objective lens.
At the same time, in the objective lens made of the resin material, an optical characteristic is easily changed depending on a temperature compared with the objective lens made of the glass material. When a numerical aperture of the objective lens is increased with increasing recording density of an optical disk, a change in optical characteristic of the objective lens has no small effect on a recording/reproduction characteristic. Particularly, in a recently-developed BD (Blu-Ray Disc), because a laser beam is collected onto the optical disk having a cover thickness of 1 mm using a high-NA objective lens whose numerical aperture is about 0.85, the slight change in optical characteristic of the objective lens has a large effect on quality of the recording/reproduction characteristic.